<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<script>
		
		window.onload=function(){

			input = document.getElementsByTagName("input");

			input[0].onclick = function () {
				if(input[0].value=="开始"){
					input[0].value = "停止"
				}else{
					input[0].value = "开始"
				}
			}
		}
	</script>
</head>
<body>
	<input type="button" value="开始">
</body>
</html>